add Apps endpoint /apps/installations/:installation_id:

Author: jamiehuson

lib/Github/Api/Apps.php

@@ -53,6 +53,19 @@ public function findInstallations()
         return $this->get('/app/installations');
     }
 
+    /**
+     * Get an installation of the application
+     *
+     * @link https://developer.github.com/v3/apps/#get-an-installation
+     *
+     * @param $installation_id An integration installation id
+     * @return array
+     */
+    public function getInstallation($installation_id)
+    {
+        return $this->get('/app/installations/'.rawurldecode($installation_id));
+    }
+
     /**
      * List repositories that are accessible to the authenticated installation.
      *

test/Github/Tests/Api/AppTest.php

@@ -27,7 +27,7 @@ public function shouldCreateInstallationTokenForInstallation()
     /**
      * @test
      */
-    public function shouldFindRepositoriesForApplication()
+    public function shouldFindInstallationsForApplication()
     {
         $result = ['installation1', 'installation2'];
 
@@ -40,6 +40,22 @@ public function shouldFindRepositoriesForApplication()
         $this->assertEquals($result, $api->findInstallations());
     }
 
+    /**
+     * @test
+     */
+    public function shouldGetInstallationForApplication()
+    {
+        $result = ['installation1'];
+
+        $api = $this->getApiMock();
+        $api->expects($this->once())
+            ->method('get')
+            ->with('/app/installations/1234')
+            ->willReturn($result);
+
+        $this->assertEquals($result, $api->getInstallation('1234'));
+    }
+
     /**
      * @test
      */